I think they didn't do this initially because it is more likely that people will be using square sizes (also goes for the view-type procs).
I also find it strange that they use bound_width and bound_height but didn't document the "bounds" variable.

It's still pretty easy to convert the text string to the two numbers with code, as you know, but more consistency in the syntax wouldn't hurt.

Of course, these _x/y variables would all be better off declared as vectors...